Thermal Aware Management

The need to develop thermal-aware management specifically for
cyber-physical systems (CPSs) has growing significance for several reasons:

First, the high cost of designing and manufacturing microprocessors
deters the design of special-purpose controllers for most CPSs.
As demanding CPS applications migrate from cost-insensitive
applications such as aerospace to highly cost-sensitive applications
such as automobiles, the pressure grows for inexpensive solutions.
Thus, it has become a common practice to use high-volume
general-purpose microprocessors as commercial
off-the-shelf components since they are considerably cheaper.
The emergence of low-cost multicore chips further enforces this
trend as complex CPSs often require multiple processors.

However, these commodity processors have not been designed
for real-time applications (often with stringent timing constraints) and
their only thermal-related concern is to ensure that cores do not
experience a thermal breakdown.
To this end, almost all contemporary processors have built-in protection
against overheating either through reduction of the voltage/frequency,
or in more severe cases, idling the overheated processor.
In general-purpose computing systems, reducing the speed of computation,
insuring a brief idle period of a single core, or even idling
the entire multicore to allow it to cool down is acceptable.
If not anticipated, such steps may negatively
impact the CPS performance and may, in certain situations,
result in failure of its mission/applications.

Thermal-aware management is a must in the case of CPSs that operate
in hot environments, such as engine compartments or
robots in harsh search-and-rescue conditions.
A higher ambient temperature reduces the temperature gradient
between the chip and its environment, slowing the rate at which
the heat can be dissipated.
This results in a higher steady-state chip temperature for the same
amount of internal heat dissipation.
Off-the-shelf multicores are not hardened for use in high-temperature
regimes unlike some specially-designed electronics components for
automotive control systems (prototypical CPSs) that are often rated
up to $140^o$C.

Even for other CPSs that normally are not expected to experience
high ambient temperatures, efficient thermal-aware
management can be beneficial.
These include CPSs for life-critical applications (e.g.,
commercial airliners' fly-by-wire systems) where the reduced reliability
that comes with continuous excessive heating is often unacceptable.

We are developing algorithms
and software implementations for CPS thermal-aware management.
Integrated, holistic, CPS management requires co-regulation
of task processing as well as
physical actions since an optimal and robust CPS must adjust both to meet
task-level objectives given models of both cyber-side
and controlled-plant-side temporal, energy, and thermal
dynamics, as well as costs and constraints.
We are devising a highly adaptive, reliability-aware, and
application-driven approach to thermal-aware management of CPSs.